1. Field of the Invention
The present invention relates to an organic EL display device, and more particularly to a technique which is effectively applicable to an organic EL display device which can prolong a lifetime thereof and can enhance reliability thereof by suppressing the degradation of an organic EL layer attributed to moisture.
2. Description of the Related Art
As a flat-panel-type display device, a liquid crystal display device (LCD), a plasma display device (PDL), a field emission type display device (FED), an organic EL display device (OLED) and the like have been put into practice or have been studied for future practical use. Among these display devices, the organic EL display device which is a typical example of a thin and light-weighted self-luminous display device is an extremely prospecting display device as a future display device.
The organic EL display device is classified into a so-called bottom-emission-type organic EL display device and a top-emission-type organic EL display device. In the bottom-emission-type organic EL display device, an organic EL element is constituted of a light emitting mechanism which is formed by sequentially stacking a transparent electrode (ITO or the like) which constitutes a first electrode or one electrode, a multi-layered organic film which emits light by applying an electric field thereto (also referred to as a organic light emitting layer), and a metal electrode having reflective property which constitutes a second electrode or another electrode on an insulation substrate which is preferably formed of a glass substrate. A large number of organic EL elements are arranged in a matrix array and another substrate or a sealing film which is referred to as a sealing can and covers the stacked structure is provided to interrupt the above-mentioned light emitting structure from an external atmosphere. Then, for example, by using a transparent electrode as an anode and a metal electrode as a cathode electrode and by applying an electric field between both electrodes, carriers (electrons and holes) are injected into the organic multi-layered film so as to allow the organic multi-layered film to emit light. This emission of light is radiated to the outside from a glass substrate side.
On the other hand, the top-emission-type organic EL display device is configured such that the above-mentioned one electrode is formed of a metal electrode having a reflective property and the above-mentioned another electrode is formed of a transparent electrode made of ITO or the like, an electric field is applied to both electrodes to allow the light emitting layer to emit light, and the light is radiated to another electrode side. In the top-emission-type organic EL display device, a transparent plate which is preferably formed of a glass plate may be used as the sealing can in the bottom-emission-type organic EL display device.
Such an organic EL display device has a drawback that an organic film which constitutes the light emitting layer is easily degraded due to moisture. Conventionally, a desiccant (a drying agent) is arranged in the inside of the sealing can or the sealing film.
FIG. 9 is a general cross-sectional view of an essential part of the organic EL display device having the conventional sealing can structure. The organic EL display device is configured such that an organic light emitting layer OLE is formed on a main surface (inner surface) of a glass substrate SUB which constitutes an insulation substrate, an upper layer of the organic light emitting layer OLE is covered with a sealing can CEL which forms a desiccant DSC on an inner surface thereof by way of a vacuum layer or an inactive gas layer VN from above, and a rib LB which is formed on a periphery of the sealing can CEL is fixedly mounted on the glass substrate SUB by an adhesive layer SEL.
With respect to this type of organic EL display device, patent document 1 discloses an organic EL display device which covers an organic light emitting layer with an insulation layer and an oxygen/moisture reaction layer and covers the organic light emitting layer with a resin layer thus sealing the organic light emitting layer. Patent document 2 discloses the organic EL display device by arranging a predetermined gas removing agent along a sealing material. Further, patent document 3 discloses the organic EL display device which seals an element by sandwiching a high moisture-absorbent film with low moisture-absorbent film.
Patent documents 1: JP-A-2000-348859
Patent documents 2: JP-A-2001-307872
Patent documents 3: JP-A-2001-357973